INVESTIGATING THE EFFECT OF CILIARY BODY PHOTODYANMIC THERAPY IN MICE

Abstract

Abstract: : Purpose: Glaucoma is often associated with raised intraocular pressure (IOP), which is a risk factor for optic nerve damage and loss of visual field. Previous studies of transscleral ciliary body photodynamic therapy (PDT) in rabbit eyes using the photosensitizer CASPc have shown a decrease IOP for 2 weeks after treatment. In this study we investigated the effect of verteporfin ciliary body PDT on IOP in normal mouse eyes. Methods: C57/BL6 mice aged 3 months were used in this study. The IOP was measured using a previously reported applanation tonometer with a fiber optic pressure sensor. Transscleral irradiation of the ciliary body was performed using a 600 µm optical fiber with applications for 360 degrees of the corneoscleral limbus, treating one eye and using the fellow eye as a control. A verteporfin dose 2.0 (n=7) or 4.0 (n=7) mg/kg was used and a fluence of 100 J/cm² using 689 nm laser light. Retreatment at 7 days after the first PDT was performed using the same light parameters in the group treated with 2.0 mg/kg of verteporfin. The IOP was measured twice a week. Eyes were processed for light microscopic examination at 1 and 7 days after treatment and at the end of follow–up (8 weeks). Results: There were no significant differences between the mean baseline IOP of treated eyes and control eyes. The mean IOP of treated eyes was significantly reduced at 24 hours after treatment in both the 2– and 4– mg/kg treated groups compared to the control eyes, by 37.1% and 35.9% respectively. The mean IOP of 2.0 mg/kg–treated group returned to the level of the fellow control eyes by 7 days after treatment. However, retreatment significantly reduced the IOP, which lasted 1 week. The mean IOP of 4.0 mg/kg–treated group returned to the normal level by 17 days after treatment. On histopathological examination, blood vessels within the ciliary body were thrombosed and the epithelium showed vacuolization at 24 hours after PDT. Conclusions: Ciliary body PDT significantly reduced the IOP in mouse eyes. These results suggest that ciliary body PDT may lead to a new cyclodestructive technique with potential clinical application in the treatment of glaucoma.

Keywords: photodynamic therapy • ciliary body • intraocular pressure